1. Field of the Invention
This invention is concerned with the preparation of a lithium complex soap grease having a high dropping point. Lithium soap greases have been known and widely used for many years. The principal advantages of a lithium soap grease have included high water resistance and ease of dispersion of the soap in all types of lubricating oil base stocks. While the lithium soaps used as thickening agents for these greases can be prepared by reaction of lithium hydroxide or other lithium base with conventional high molecular weight fatty acids, lithium 12-hydroxy stearic acid and the lithium soaps of related hydroxy fatty acids have been particularly useful because of their great mechanical stability.
There are many fields of application of grease compositions where a high dropping point is required, as for example in the lubrication of automotive disc brake wheel bearings. Such disc brakes are used in modern locomotives.
The prior art discloses batch processes for preparing high dropping point lithium complex soap greases. One known process requires separate saponification steps for the monocarboxylic fatty acid and for the dicarboxylic fatty acid components. In another process, the monocarboxylic acid and dicarboxylic acid components are saponified together but this process requires at least two distinct heating steps following the saponification step in order to complete grease formation.
Improved complex soap process for preparing high dropping point lithium greases, having fewer steps would be commercially advantageous and desirable.
An object of this invention is to provide a process for preparing lithium complex soap greases which will provide substantial advantages in convenience and economy over known methods.
2. Description of the Prior Art
U.S. Pat. No. 3,681,242 discloses a batch process for preparing a high dropping point lithium complex soap grease which includes two distinct heating stages after saponification. The lithium soap is prepared from a mixture of C.sub.12 to C.sub.24 hydroxy fatty acid and a C.sub.4 to C.sub.12 dicarboxylic acid.
U.S. Pat. No. 3,791,973 discloses a batch process for preparing a high dropping point lithium complex soap grease by a particular sequence of steps which includes the separate formation of the lithium soaps of C.sub.12 to C.sub.24 hydroxy fatty acid and of a C.sub.4 to C.sub.12 aliphatic dicarboxylic acid.